A method and system for suppressing load disturbance of binary distillation tower

Abstract

The present invention discloses a method and system for suppressing load interference of a binary distillation tower. The method for suppressing load interference establishes a mathematical model of a binary distillation tower by identifying the transfer function of the control channel between each input and output; effectively estimates the external load interference based on the obtained mathematical model of the distillation tower and the input and output data, and then designs a performance filter to improve the dynamic performance of interference suppression; finally, the adjustment signal output by the interference estimation signal after passing through the performance filter is used as the system adjustment control input. The present invention is simple and easy to implement, and can effectively control a binary distillation tower with load interference, reduce the impact of interference on the system, and thus improve the quality of products extracted from the top and bottom of the tower.

Description

Technical Field

[0001] The invention relates to automatic control of a distillation tower, and in particular to a method and system for suppressing load interference of a binary distillation tower. Background Art

[0002] In the petrochemical industry, product purification and recovery are mostly achieved through distillation. Effective control of the distillation tower is of great significance for improving distillation efficiency and saving energy. However, the distillation process is relatively complex and it is difficult to establish a more accurate mechanism model, so higher requirements are placed on the control method. Taking the binary distillation tower as an example, it is mainly used to separate a mixture containing two components. In fact, it can be abstracted as a multivariable process with two inputs and two outputs. This process has the characteristics of large lag and strong coupling, which makes the conventional control scheme need to be improved in effect. In addition, the problem of load interference suppression is also an inevitable problem in the distillation process. For example, changes in pipeline pressure and changes in feed components will have an adverse effect on the final control effect. Although conventional PID control can suppress interference to a certain extent, there are problems such as large control lag and the controller needs to compromise between multiple targets in regulation, which are not conducive to interference suppression. In traditional methods, the interference suppression effect of feedforward control is better, but the requirements for interference are higher, the interference needs to be measurable, and one feedforward control can only be applied to one interference, which has strong limitations. How to combine the advantages of feedforward and feedback to improve the interference suppression effect of binary distillation tower is a problem that needs to be solved. Summary of the invention

[0003] Purpose of the invention: The purpose of the present invention is to provide a method for suppressing load interference of a binary distillation tower with good interference suppression effect. The second purpose of the present invention is to provide a system for suppressing load interference of a binary distillation tower.

[0004] Technical solution: The method for suppressing load interference of a binary distillation tower according to the present invention comprises the following steps:

[0005] (1) Collecting input and output data of binary distillation tower;

[0006] (2) The transfer function of each control channel between input and output is identified by using the least squares identification algorithm, and the transfer function matrix model of the binary distillation tower is established as follows:

[0007]

[0008] Where s is the Laplace operator, y1 and y2 are the two controlled outputs of the binary distillation tower, u1 and u2 are the two control inputs of the binary distillation tower; the element g in the i-th row and j-th column of the transfer function matrix ij (s) represents input u j To output y iThe transfer function of the control channel, i = 1, 2; j = 1, 2; the identified g ij (s) is in the form of first order plus time lag as follows:

[0009]

[0010] Where K ij is the transfer function g ij (s) proportional gain, T ij is the transfer function g ij (s) is the inertia time constant, is the transfer function g ij (s) time lag, L ij is the lag time, e is the constant natural logarithm;

[0011] (3) Using the transfer function matrix model obtained in step (2), an interference estimation unit is designed. The estimated value of the load interference can be obtained using the interference estimation unit and the input and output data. The estimated value of the load interference can be calculated by the following formula:

[0012] W1(s)=Γ1(s)y1(s)+f 11 (s)V1(s)+f 12 (s)V2(s)

[0013] W2(s)=Γ2(s)y2(s)+f 21 (s)V1(s)+f 22 (s)V2(s)

[0014] V1(s)=q 11 (s)W1(s)+q 12 (s)W2(s)

[0015] V2(s)=q 21 (s)W1(s)+q 22 (s)W2(s)

[0016]

[0017] Among them, W1, W2, V1, and V2 are intermediate variables; and is the estimated value of load disturbance;

[0018] Γ1 and Γ2 are time-delay compensators, and the expression is τ i To compensate for the lag time;

[0019] f 11 , f 12 , f 21 , f 22is the reverse regulator of the controlled output, q 11 ,q 12 ,q 21 ,q 22 is the forward regulator of the controlled output, H1 and H2 are the forward regulators of the control input;

[0020] (4) The estimated value of the load disturbance is used as the input of the performance filter, and the output of the performance filter is used to adjust the control input of the system.

[0021] In the present invention, an effective estimation of external load interference is achieved based on the established mathematical model of the distillation tower and the collected input and output data, and the dynamic performance of interference suppression is improved through the performance filter, so that when there is load interference in the system, the influence of interference on the system output can be effectively reduced, and the quality of the products extracted from the top and bottom of the tower can be improved. In addition, the load interference suppression method is simple and easy to implement.

[0022] Furthermore, in step (1), the input and output data of the binary distillation tower are collected within a time period t, where the time period t is the time period from the moment a step signal for identifying each channel is added to the moment the output reaches a new steady-state value.

[0023] Furthermore, in step (2), according to the amplitude h of the step signal, the sampling period Ts and the output Y(k) of the acquisition process, the parameters of the transfer function of each channel are calculated according to the following formula:

[0024]

[0025] θ=(P T ·P) -1 P T Q

[0026] Where P and Q are coefficient matrices composed of h, Ts, and Y(k), respectively, and θ is a parameter used to identify the transfer function of each branch.

[0027] Further, step (3) comprises:

[0028] (301) According to the time lag of each channel in the binary distillation tower transfer function matrix, the controlled process is classified. The specific rules are as follows:

[0029] If L 11 ≤L 21 And L 22 ≤L 12 , then it belongs to “Type I”;

[0030] If L 11 >L 21 And L 22 >L 12 , then it belongs to "Type II";

[0031] If L 11 ≤L 21 And L 22 >L 12 And (L 22 +L 11 )≤(L 21 +L 12 ), it belongs to "Type III";

[0032] If L 11 ≤L 21 And L 22 >L 12 And (L 22 +L 11 )>(L 21 +L 12 ), it belongs to "Type IV";

[0033] If L 11 >L 21 And L 22 ≤L 12 And (L 22 +L 11 )≤(L 21 +L 12 ), it belongs to "Type V";

[0034] If L 11 >L 21 And L 22 ≤L 12 And (L 22 +L 11 )>(L 21 +L 12 ), then it belongs to “Type VI”;

[0035] (302) According to the type of the controlled process, the compensation delay times τ1 and τ2 of the delay compensators Γ1 and Γ2 are determined according to the following rules:

[0036] Type I: τ1=0, τ2=0;

[0037] Type II: τ1=0, τ2=0;

[0038] Type III: τ1=(L 22 -L 12 ), τ2=0;

[0039] Type IV: τ1=(L 21 -L 11 ), τ2=0;

[0040] Type V: τ1=0,τ2=(L 11 -L 21);

[0041] Type VI: τ1 = 0, τ2 = (L 12 -L 22 );

[0042] (303) According to the type of the controlled process, the forward regulator q of the controlled output is determined according to the following rules: 11 ,q 12 ,q 21 and q 22 :

[0043] Type I: q 11 =1,q 12 =0,q 21 =0,q 22 =1;

[0044] Type II: q 11 =0,q 12 =1,q 21 =1,q 22 =0;

[0045] Type III: q 11 =1,q 12 =0,q 21 =0,q 22 =1;

[0046] Type IV:q 11 =0,q 12 =1,q 21 =1,q 22 =0;

[0047] Type V: q 11 =1,q 12 =0,q 21 =0,q 22 =1;

[0048] Type VI:q 11 =0,q 12 =1,q 21 =1,q 22 =0;

[0049] (304) According to the type of the controlled process, the reverse regulator f of the controlled output is determined according to the following rules. 11 , f 12 , f 21 and f 22 :

[0050] Type I: Type II: Type III: Type IV: Type V: Type VI:

[0051] (305) According to the type of the controlled process, the control input H1 and H2 are determined according to the following rules: Type I: Type II:

[0052] Type III:

[0053] Type IV:

[0054] Type V:

[0055] Type VI:

[0056] (306) Based on the above classification, the estimated value of the load interference is obtained according to the interference estimation relationship: and

[0057] Further, step (4) comprises:

[0058] (401) Design the form of performance filters C1 and C2, where C1 and C2 are the estimated values ​​of the load disturbance respectively. and The performance filter is:

[0059] For Type I, Type III, Type V

[0060]

[0061] For Type II, Type IV, Type VI

[0062]

[0063] (402) Given the value of the robustness index Ms, the filter adjustment parameters λ1 and λ2 are obtained according to the following formula

[0064]

[0065] where β i H i The lag time, for different types of controlled processes, β i The expression is as follows

[0066] Type I:

[0067] Type II:

[0068] Type III:

[0069] Type IV:

[0070] Type V:

[0071] Type VI:

[0072] This results in the final performance filter.

[0073] On the other hand, the present invention also provides a binary distillation tower load interference suppression system, comprising a measurement transmitter and a data storage and output unit connected in sequence, and a system identification unit, an interference estimation unit and a performance filter unit are sequentially connected after the data storage and output unit;

[0074] Measuring transmitters for collecting input and output data of binary distillation columns;

[0075] A data storage and output unit, used for storing input and output data collected by the measuring transmitter, and outputting the data to the system identification unit for identifying the system model and the interference estimation unit for obtaining interference estimation;

[0076] A system identification unit is used to identify the transfer function of each channel and establish a transfer function matrix model of the binary distillation column;

[0077] The interference estimation unit is used to analyze the transfer function matrix model and obtain the interference estimation value by using the input and output data through the corresponding compensator and regulator;

[0078] The performance filter unit is used to take the interference estimation value as input and output the adjustment signal to adjust the system input. The performance filter is designed according to the transfer function matrix model and the interference estimation unit in accordance with the given robustness and dynamic performance requirements.

[0079] The load interference suppression system has a simple structure and, as mentioned above, can effectively reduce the impact of the interference on the system output when there is load interference in the system.

[0080] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: when there is load interference in the system, the influence of the interference on the system output can be effectively reduced; the load interference suppression method and system are simple and easy to implement. BRIEF DESCRIPTION OF THE DRAWINGS

[0081] Figure 1It is a flow chart of a method for suppressing load disturbance of a binary distillation column;

[0082] Figure 2 is a structural diagram of the interference estimation unit;

[0083] Figure 3 It is a structural diagram of the binary distillation tower load disturbance suppression system. DETAILED DESCRIPTION

[0084] The present invention will be further described in detail below in conjunction with the accompanying drawings.

[0085] Taking a binary distillation tower with components of methanol and water as an example, the input (controlled variable) selected in this process is the reflux flow at the top of the tower and the steam flow at the bottom of the tower, and the output (controlled variable) is the mole fraction of the methanol component at the top of the tower and the mole fraction of methanol at the bottom of the tower. The control goal is: in the presence of input load interference, the system can quickly return to the set state.

[0086] like Figure 1 As shown, a method for suppressing load interference of a binary distillation tower comprises the following steps:

[0087] (1) measuring the reflux flow value at the top of the tower and the steam flow value at the bottom of the tower from the input end of the process, measuring the methanol mole fraction at the top and bottom of the tower from the output end of the process, and converting the flow value and mole fraction into electrical signals;

[0088] (2) storing the electrical signals in step (1) until the number required for identifying each channel is met, and transmitting the electrical signals to the system identification module;

[0089] (3) identifying the transfer function of each channel according to the set least squares identification algorithm, and forming a transfer function matrix with the identified transfer functions;

[0090] After identification, the transfer function matrix is ​​obtained as follows:

[0091]

[0092] Where m1 and m2 are the mole fractions of methanol in the top and bottom products, respectively, and R and S are the top reflux flow and bottom heating steam flow, respectively.

[0093] (4) Using the identified process model, design the interference estimation unit.

[0094] First, the process model is classified according to the time delay of each channel. In this example, L 11 =1,L 12 =3,L 21 =7,L 22 =3, which meets the conditions of Type I, and therefore belongs to Type I.

[0095] Determine the form of the time-delay compensator. Since the controlled process belongs to type I, the compensation delay time τ1 = 0 and τ2 = 0 can be determined, and then the time-delay compensator Γ1 = 1 and Γ2 = 1 can be determined, that is, no additional time-delay compensation is required.

[0096] Determine the forward regulator q of the controlled output 11 ,q 12 ,q 21 and q 22 Since the controlled process belongs to type I, according to the rules, the forward regulator can be determined to be q 11 =1,q 12 =0,q 21 =0,q 22 =1.

[0097] Determine the reverse regulator f of the controlled output 11 , f 12 , f 21 and f 22 Since the controlled process belongs to type I, according to the rules, the reverse regulator can be determined as

[0098]

[0099] Determine the forward regulators H1 and H2 of the control input. Since the controlled process belongs to type I, according to the rules, the forward regulator of the input can be determined as

[0100]

[0101] Using the designed parts, the estimated value of the load interference is calculated according to the following interference estimation relationship: and The following relationship can be obtained through Figure 2 accomplish. Figure 2 This is a structural diagram of an interference estimation unit. An interference estimation value can be obtained by inputting system input and output data in a data storage unit.

[0102]

[0103] V1(s)=W1(s)

[0104] V2(s)=W2(s)

[0105]

[0106] W1, W2, V1, V2 are intermediate variables.

[0107] (5) designing a performance filter according to the transfer function matrix model obtained in step (3) and the interference estimation unit obtained in step (4) in accordance with given robustness and dynamic performance requirements;

[0108] Since the controlled process belongs to type I, according to the rules, the performance filter designed is

[0109]

[0110] Given the robustness index Ms = 1.4, the rules give β1 = 1 and β2 = 3, and the adjustable parameters of the performance filter can be determined as:

[0111]

[0112] Using the obtained parameters λ1 and λ2, the final performance filter can be determined:

[0113]

[0114] (6) Using the designed performance filter and the estimated value of the interference, the system's top tower reflux flow and the tower bottom heating steam flow are adjusted.

[0115] like Figure 3 As shown, it includes a binary distillation tower and a binary distillation tower load interference suppression control system, and the binary distillation tower load interference suppression control system includes:

[0116] A measuring transmitter is used to measure the reflux rate at the top of the tower, the heating steam rate at the bottom of the tower, and the molar fraction of methanol produced at the top and bottom of the tower, and to convert the above parameters into electrical signals;

[0117] The data storage and output unit stores the signal from the measuring transmitter and outputs it to the system identification unit to identify the system model and the interference estimation unit to obtain the interference estimation;

[0118] A system identification unit, used to identify the transfer function of each channel through calculation to form a transfer function matrix of the binary distillation column;

[0119] The disturbance estimation unit analyzes the transfer function matrix of the process, obtains the disturbance estimation value through the corresponding compensator and regulator, and uses the input and output data;

[0120] The performance filter unit is used to take the interference estimate as input and output a conditioning signal to condition the system input.

Claims

1. A method for suppressing load interference of a binary distillation tower, characterized in that: The steps include: (1) Collecting input and output data of binary distillation tower; (2) The transfer function of each control channel between input and output is identified by using the least squares identification algorithm, and the transfer function matrix model of the binary distillation tower is established as follows: Where s is the Laplace operator, y1 and y2 are the two controlled outputs of the binary distillation tower, u1 and u2 are the two control inputs of the binary distillation tower; the element g in the i-th row and j-th column of the transfer function matrix ij (s) represents input u j To output y i The transfer function of the control channel, i = 1, 2; j = 1, 2; the identified g ij (s) is in the form of first order plus time lag as follows: Where K ij is the transfer function g ij (s) proportional gain, T ij is the transfer function g ij (s) is the inertia time constant, is the transfer function g ij (s) time lag, L ij is the lag time, e is the constant natural logarithm; (3) The load disturbance is estimated using the input and output data and the transfer function matrix model. The estimated value of the load disturbance can be obtained by the following formula: W1(s)=Γ1(s)y1(s)+f 11 (s)V1(s)+f 12 (s)V2(s) W2(s)=Γ2(s)y2(s)+f 21 (s)V1(s)+f 22 (s)V2(s) V1(s)=q 11 (s)W1(s)+q 12 (s)W2(s) V2(s)=q 21 (s)W1(s)+q 22 (s)W2(s) Among them, W1, W2, V1, and V2 are intermediate variables; and is the estimated value of load disturbance; Γ1 and Γ2 are time-delay compensators, and the expression is τ i To compensate for the lag time; f 11 , f 12 , f 21 , f 22 is the reverse regulator of the controlled output, q 11 ,q 12 ,q 21 ,q 22 is the forward regulator of the controlled output, H1 and H2 are the forward regulators of the control input; (4) using the estimated value of the load disturbance as the input of the performance filter, and using the output of the performance filter to adjust the control input of the system; Step (3) includes: (301) According to the time lag of each channel in the binary distillation tower transfer function matrix, the controlled process is classified. The specific rules are as follows: If L 11 ≤L 21 And L 22 ≤L 12 , then it belongs to "Type I"; If L 11 >L 21 And L 22 >L 12 , then it belongs to "Type II"; If L 11 ≤L 21 And L 22 >L 12 And (L 22 +L 11 )≤(L 21 +L 12 ), it belongs to "Type III"; If L 11 ≤L 21 And L 22 >L 12 And (L 22 +L 11 )>(L 21 +L 12 ), it belongs to "Type IV"; If L 11 >L 21 And L 22 ≤L 12 And (L 22 +L 11 )≤(L 21 +L 12 ), it belongs to "Type V"; If L 11 >L 21 And L 22 ≤L 12 And (L 22 +L 11 )>(L 21 +L 12 ), then it belongs to "Type VI"; (302) According to the type of the controlled process, the compensation delay times τ1 and τ2 of the delay compensators Γ1 and Γ2 are determined according to the following rules: Type I: τ1=0, τ2=0; Type II: τ1=0, τ2=0; Type III: τ1=(L 22 -L 12 ), τ2=0; Type IV: τ1=(L 21 -L 11 ), τ2=0; Type V: τ1=0,τ2=(L 11 -L 21 ); Type VI: τ1 = 0, τ2 = (L 12 -L 22 ); (303) According to the type of the controlled process, the forward regulator q of the controlled output is determined according to the following rules: 11 ,q 12 ,q 21 and q 22 : Type I: q 11 =1,q 12 =0,q 21 =0,q 22 =1; Type II: q 11 =0,q 12 =1,q 21 =1,q 22 =0; Type III: q 11 =1,q 12 =0,q 21 =0,q 22 =1; Type IV:q 11 =0,q 12 =1,q 21 =1,q 22 =0; Type V: q 11 =1,q 12 =0,q 21 =0,q 22 =1; Type VI: q 11 =0,q 12 =1,q 21 =1,q 22 =0; (304) According to the type of the controlled process, the reverse regulator f of the controlled output is determined according to the following rules. 11 , f 12 , f 21 and f 22 : Type I: Type II: Type III: Type IV: Type V: Type VI: (305) According to the type of the controlled process, the control input H1 and H2 are determined according to the following rules: Type I: Type II: Type III: Type IV: Type V: Type VI: (306) Based on the above classification, the estimated value of the load interference is obtained according to the interference estimation relationship: and 2. The method for suppressing load disturbance of a binary distillation tower according to claim 1, characterized in that: In step (1), the input and output data of the binary distillation tower are collected within a time period t, where the time period t is the time period from the moment a step signal for identifying each channel is added to the moment the output reaches a new steady-state value.

3. The method for suppressing load disturbance of a binary distillation tower according to claim 2, characterized in that: In step (2), according to the amplitude h of the step signal, the sampling period Ts and the output Y(k) of the acquisition process, the parameters of the transfer function of each channel are calculated according to the following formula: θ=(P T ·P) -1 P T Q Where P and Q are coefficient matrices composed of h, Ts, and Y(k), respectively, and θ is a parameter used to identify the transfer function of each branch.

4. The method for suppressing load disturbance of a binary distillation tower according to claim 1, characterized in that: Step (4) comprises: (401) Design the form of performance filters C1 and C2, where C1 and C2 are the estimated values ​​of the load disturbance respectively. and The performance filter is: For Type I, Type III, Type V For Type II, Type IV, Type VI (402) Given the value of the robustness index Ms, the filter adjustment parameters λ1 and λ2 are obtained according to the following formula where β i H i The lag time, for different types of controlled processes, β i The expression is as follows Type I: Type II: Type III: Type IV: Type V: Type VI: This results in the final performance filter.

5. A system for implementing the method for suppressing load disturbance of a binary distillation tower according to claim 1, characterized in that: include: Measuring transmitters for collecting input and output data of binary distillation columns; A data storage and output unit, used to store input and output data collected by the measuring transmitter and output it to the system identification unit and the interference estimation unit; A system identification unit is used to identify the transfer function of each channel and establish a transfer function matrix model of the binary distillation column; The interference estimation unit is used to analyze the transfer function matrix model and obtain the interference estimation value by using the input and output data through the corresponding compensator and regulator; A performance filter unit is used to take the interference estimate as input and output a conditioning signal to condition the system input.

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